Turbine



Jan. 9, 1934. F. LJuNGsTRM 1,942,608

- y TURBINE Filed sept. 8, 195; 6 sheets-sheet 1 OLAvE-on- Jan. 9, 1934.F. LJuNGsTRM 1,942,608y

TURBINE l Y' Filed Sept. 8, 1931 I 6 Sheets-Sheet 2 INVENTO l 6Sheets-Sheet 3 y Jan. 9, 1934. F. LJUNGSTRM TURBINE Filed sept. 8,1951'.

lll l Jan. 9, 1934. l F. I JUNGSTROM 1,942,608 Y TURBINE l Filed Sept.8. 1931 6 Sheets-Sheet 4 mvE ToR N I ZVWA Jan.9,1934. F1 LJUNGSTRM1,942,608

TURBINEA Filed spi. 8, 1931 e sheets-sheet e l INVENT R I r; ATTORNEYPatented Jan. 9, 1934 UNITED STATES PATENT OFFICE` TURBINE FredrikLjungstrm, Brevik, Lindingo,

assignor to Aktiebolaget Spontan, Sweden, a corporation of SwedenSweden, Stockholm,

Application September 8, 1931, Serial No. 561,565,

and in Germany September 15, 1 930 46 Claims.

pressure, which may be a vacuum, and the power output. 'I'hese factorstaken together, will, in

general, determine the quantity of steam. Steam will theoreticallyexpand according to inherent l characteristics or laws ofthermodynamics.

Having selected the general thermodynamic conditions under which thesteam is to act (adiabatic expansion, impulse, reaction, etc.) `thedesigners task is to adapt the design to the most eflicient utilizationof the steam. But he has not been entirely free in this respect becauseof limitations of structural nature, principally in limits of stress andstrain of materials. Generally speaking, these limitations have'prohibited the best -utilization of steam expansion, and a vcompro--mise has resulted between the most efficient expansion path for thesteam and structural requirements. This situation is usually expressedby the statement that due to structural limi- '.35 tations it isimpossible to construct the last or later stages of a turbine to mosteiciently utilize the steam, a statement which is obviously based on apredetermined selection of size -and other characteristics.

Y The limiting factors involve centrifugal stresses and stresses due tovibration both in later stage wheels or bond rings and blades attachedthereto. These factors have been considered as necessary evils and4various mechanical expedients have been devised to offset them. Myinvention aims to utilize these structural factors as assisting factors,rather than opposing factors, in adapting the path of steam flow tosteamconditions. Inrthe. preferred form of my invention, I utilizecentrifugal force to determine the shape and contour of someof theblades.

In my;Patent No. 1,897,172, granted Feb. 14, 1933 on' myfcopendingapplication'filed August 16, 1929, I havedisclosed a turbine havingoutwardly curved low pressure blades designed to permit increased flowarea with relatively small stresses in the blades and in the bladecarrying parts. In the structure therein disclosed, blades ofsubstantially uniform cross-section are used which are curved betweenthe points of attachmentin suchl manner that, when the blades arerotated' in operation,'only or substantially only tension (orcompression) stresses exist in the blades. The blades therein are of' across-section S51/of the general character used in turbines; that is,

(ci. 25a-16.5)

the blades are thicker in the midd1e enana@ theI inlet or outlet edges.In designing blading in accordance with the disclosure of myiai'oresaidcopending application, the proper curvature is first calculated, whichcan be readily done from knowledge of the various factors, and then theblades are formed tov conform to such curvature so that when the turbineis rotated at the intended speed, the blades` will be stressed onlylongitudinally, as in a freely suspended rope, .W forming what is knownas a catenary curve. In` my aforesaid application, however, the bladesare designed as rigid blades.

The present invention constitutes an improvement'over what is shown inmy aforesaid appli- 70 cation, the major feature of the presentinvention consisting in the provision of light blades of flexiblematerial such that of themselves they do not have the requisite rigidityfor reacting against the steam. The blades are supported at 7G axiallyspaced points and are longer Ithan the distance between the points ofattachment.- In operation they are given their shape` due to centrifugalforce. Thus, I employ the basic principle of the aforesaid applicationwhereby a long 30 blade is obtained while stresses in the retainingmembers are kept at a minimum, the retaining members being at aconsiderable distance radially4 inward of the outward portions of theblades, and I provide blades which are of very light construction andwhich are preferably made of. thin sheet metal, which blades, althoughof themselves iiexible and bendable in natural state, form rigidly'acting blades when rotated in the turbine.

As a subsidiary feature of the invention, I provide novel means forsecuring blades in retaining members, wheels or lbond rings.

Another feature of my invention is a combined axial flow and radial flowturbine efficiency and very small weight per unit power. output. f v fMy invention will be furtherexplained by refe erence to the accompanyingdrawings fqrliins a part of this specification, with respect to which:100

Fig. 1 is anaxialsectional view of a turbine of the radial ow typeembodying Athe inventlon,- and'is taken on'the line 1-1 of Fig. 2; i vFig. 2 is a transverse view normal tothe axis the line 2-2 of Fig. 1;

Fig. 3 is a developed peripheral view taken on the line 3 3 of Fig. 2showing one blade in full,

Fig. 4 is a view similar to Fig. 2 cfamodified of rotation of the sameturbine, and is taker;v on mi form of blade;

of very high Fig. 5 shows how blades in accordance with of rotation;

Fig. 8 shows a turbine of the radial ilow type having but one row offlexible blades and a row of xed guides;

Fig. 9 is an axial cross-sectional view, somewhat diagrammatic, of acombined axial flow and radial iiow turbine embodying the invention;

Fig. 10 is an enlarged view of the lower pressure stages of the turbineshown in Fig. 9;

Fig. 11 is a transverse sectional view taken on the line 11-11 of Fig.9;

Figs. 12, 13 and 14 are views similar to Fig. l0,v

but more diagrammatic, of modified constructions;

a combinedaxial flow and radial flow turbine embodying the invention andhaving paths of ilow directed toward each other from separate inlets toa common outlet; and

Fig. 16 shows, more or less diagrammatically, a combined axial flow andradial flow turbine embodying the invention having two rows of laststage blades through which steam passes in parallel.

Referring more particularly to the embodiment shown in Figs. 1, 2, 3, 5and 6, reference characters 10 and 11 designate oppositely rotatingcoaxially mounted wheels or discs of a radial ow turbine. Annularrotors12, 13, 14, 15 and 16 are alternately supported by and rotate with discs10 and 11 by means of expansion rings 9. Rotors 12 to 16 each comprisetwo blade retaining rings between which the blades extend and into whichthe blades are secured. The blades 17 carried by member 12 are disposedas shown in Fig. 2 so that member 12 rotatesas indicated by the arrow atthe right of Fig. 2. The blades 18 of the next radially outward rotorare oppositely curved so that rotation is in the opposite direction asindicated by the arrow at the right of Fig. 2. Thus, alternate rotorsrotate together in one direction and the intermediate alternate rotorsrotate in the opposite direction. The blades carried by members 12 to 16are straight, rigid blades as shown in Fig. 1, having cross-sections asshown in Fig. 2. This represents known turbine' construction and may beused for the earlier stages of a turbine embodying my invention. f

Rotors 21, 22, 23 and 24 include blades embodying the present invention.Rotors 21 and 23 are connected by expansion rings to a member 25connected to disc 10 to rotate therewith. Rotors 22 andv 24'areconnected by expansion rings to a member 26 connected to disc 11 torotate therewith. Thus rotors 22 and 24 rotate in opposite direction torotors 21 and 23. Each of these rotors 21, 22, 23 and 24 comprises twosubstantially similar blade retaining members or rings 27 having outersurfaces 28 oblique to the axis of rotation. Stays 29 extend obliquelybetween the blade retaining rings 2'1 and are secured thereto as bywelding. (See Fig. 3.) Stays 29 are preferably welded to or integrallyformed with peripheral reinforcing strips or bands 30, thereby formingan axially extending stiffening web structure between the bladeretaining rings of each rotor carrying the curved blades, that is, theblades bent outwardly in accordance with the invention, and maintainingthe retaining rings a fixed distance apart. The blades of rotor 21 arenumbered 31; the blades of rotor 22 are numbered 32; the blades of rotor23 are numbered 33; and the blades of rotor 24 are numbered 34.4 I willdescribe the blades 34 in detail and it will be understood that theblades 31, 32 and 33 are similar to blades 34 but of less outwardcurvature, the lengths of the blades being selected to give the correctwidth of path of flow of steam for the respective stages.

The blades 34 are made of thin strips of sheet material, preferablystainless steel. Fig. 5 shows how these blades may be cut from a sheetof steel. The theory underlying the form of these blades is that of thecatenary. The catenary curve is that curve assumed by a flexible rope orthe like freely suspended between to points of attachment and of longerlength than the straight line distance between the points of attachment.This curve is such that the suspended member is subjected only tolongitudinal stressesthat is,.no'

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terial to give a suitable curve as shown in Fig..

the inlet edges 36 and the outlet edges 37 are curved outwardly betweenthe points of attachment. The blades are preferably so cut from thesheet material and so held in the retaining members that each inlet andoutlet edge lies in a single plane. These planes may be parallel asshown in Fig. 2; or they may diverge from the axis of rotation as acenter, as shown at 34a in Fig. 4; or they may converge away from theaxis of rotation, in which last case they may overlap at the points ofattachment as shown in Fig. 7a. When formed and mounted, all the surfacelines of the blades in axial planes are curved and all the surface linesin radial planes are substantially straight. Blades according to theinvention, if removed from the turbine should return to or toward or bereadily bent to their original flat shape.

With the present invention the blades can be designed to give anydesired cross-sectional area of flow therebetween-with the best selectedangles to suit the steam expansion. At the same time, the retainingmembers are relatively near the center of rotation and the stresses inthese members are kept at a minimum. The stresses in the bladesthemselves are best suited to the structure, and blading of minimumthickness can be utilized.

Fig. 3 shows the oblique grooves 40 in the blade retaining members intowhich the ends of the blades are tted. It will be seen that the groovesare of opposite angular relationship with respect to the axis ofrotation. Fig. 6 shows one method of retaining the blades in thegrooves. The grooves 40 areundercut to forni a fulcrum or pivot recessat 41. The ends of the .blades are bent over or curved to fit thegrooves. After the end of the blade is placed in the groove, a key orwedge 42 discs. The turbine is shown as coupled to and drivinganvelectric generator 59, though it will be understood that it may driveany type of rotatable power consumer.

After the steam passes through the axial blade system, it enters a spaceand thence ilows radially through guides 61, blades 62, guides 63 andblades 64. After leaving blades 64, the steam passes out at 65 to thecondenser. The guides 61 and 63 and the blades 62 and 64 constitute whatI term a radial blade system. These parts are shown more in detail inFigs. 10 and 11.

Secured to the main part of the casing 53 isl an annular member 65 whichcarries two axially spaced rings 66 and 67 into which are set the guides63. The cross-sectional character of these guides is shown in Fig. l1.Rings 68 and 69 and guides 61 set thereinto are also fixed to ring 65.It will be seen that rings 67 and 69 are supported only through guides63 and 61 respectively.

Mounted on the rotor 54 is a member 70 which is secured thereto by aclamping ring 71 screwed onto the rotor and which may be keyed vonto therotor. Member may be termed a rotor flange and extends radially outwardbeyondring 67. Blades 62 are secured in retaining rings 72 and 73 andring 73 is secured to flange member 70 by an expansion ring 74. Blades64 are secured in rings 75 and 76 of which ring 76 may be integral withflange member 70. Stay members 29-30 connect rings 72 and 73. Similarstay members connect rings 75 and 76.

After the steam has passed through `the axial blade system in knownmanner, it passes radially through the stationary guide member composedof the rings 68 and 69 and the guides 61 connecting the same. The steamthen passes through the radial flow rotorcomprising the retaining' rings72 and 73, the outwardly curved iiexible blades 62 connected thereto andthe stay members 29--30 connecting the rings 72 and 73. The steam thenpasses through another stationary guide member comprising rings 66 and67 and the connected guides 63. The steam then passes through thelast'radial flow rotor made up of the rings 75 and 76, the intermediateconnected structure 29-30, and the blades 64 connected thereto. Theblades 63 and 64 are in all essential respects similar to the blades 33and 34 respectively of Fig. 1. The blades may be secured to theretaining members in the manner shown in Fig. 6 or Fig. 7.

Fig. 9 clearly shows how the invention provides a large blade area at anVoutward radial point while the same is supported by carrying memberswhich are radially much nearer theaxis of rotation. In effect, thesteam, before it passes to the condenser, passes between a series ofbands thrown or held outwardly a considerable distance, much as a childsjump rope, the bands being made of at strips of steel and having shorterfront edges than rear edges.

It will also be evident from Fig. 9 that an axial turbine of knownconstruction can be converted to embody the invention and therebyincrease its capacity to a very great extent. With many axial turbinesit would be a simple expedient to remove some of the later axial owstages and add -a flange member 70 and provide radial blading inaccordance with the invention. The possibilities of the invention inproviding extremely long blades without intermediate support are clearlyshown in Fig. 9.

The turbine may be equipped with variousauxdial ow of fluid to saidblade.

iliaries vsuch as a bleed line 'I8 for extracting steam between stages.The extraction of steam is much more adaptable to an axial ow turbinethana radial ilow turbine, and the adaptability of the invention to anaxial flow turbine facilitates bleeding. The turbine may also beequipped as shown in Fig. 9 with intermediate stage admission, forexample, through a passage 79 controlled by a valve 80.

The arrangement shown in Fig. 12 differsv from that shown in Fig. 10only in that instead of using axially extending guides 61, the axial owsystem is provided with a last row of radial guides 57a. Thus the steamenters chamber 60 from between stationary guides and passes directly toblades 62. It will be obvious that the guides 57a may be placed atvarious positions between the last movable blades of the axial bladesystem and the iirsrJ movable blades of the radial blade system.

In Fig. 13 the radial flow system includes one row of blades 64. Aheadof this row is an axially disposed set of guides 63. In this case, asinFig. 10, the last steam directing members of the axial system arerotatable blades. Fig. 14 differs from Fig. 13 only in that the guidesahead of the single row of blades 64 are in the axial flow system,extending radially inwardly from the casing 53.

Comparison of Figs. 9 to 14 will show thata' standard turbine rotor andcasing can be designed and by relatively simple changes in structure andrelation of parts of the axial flow system to the radial ow system, agreat variation in capacities can be obtained. Thus the invention aidsin the standardization of manufacture and cheapening of manufacture ofturbines in general. Steam may be bled from chamber 60 and it will beunderstood that the pressure' in this chamber will vary depending on theselection of arrangements shown in Figs. 9 to 14.

Fig. 15 shows an embodiment of the invention in which there are twoaxial blade systems and two radial blade systems in parallel. The rotorhas an intermediate flange 80 whichy carries two sets of blades'64. Theouter portion 81 is an intermediate member of a cylindrical rotary webstructure including also rings 82 and 83 and the intermediate staystructure 29--30. One group of blades is secured to ring 82 and ange 80and the other group is secured to ring 83 and iiange 80. Steam flowsfrom separate inlets through the axial blade systems and in parallelthrough radial blade systems, the paths joining at the exits of theblades 64 in lthe casing 84.

Fig. 16 shows a single axial blade system with two radial blade systemsin parallel. In this form, holes 85 are provided in ange 80 and the flowis in the direction indicated by the arrows.

While I have shown and described a variety of forms of embodiment of myinvention, it will be understood that many other embodiments arepossible Within the vention.

What I claim is:

1. In a turbine, axially spaced rotatable blade retaining members, ablade consisting of a relatively thin iiexible strip of material securedto said members, and means providing a radial flow of fluid to saidblade.

2. In a turbine, axially spaced rotatable blade retaining members, ablade of structurally exible formation secured to said members andadapted to change its form under the influence of centrifugal force, andmeans providing a raspirit and -scope of the inportion to such `anextent as-to bend the blade into the undercut recess 4l. Centrifugalforce tends to pull, the blade 34 out of the groove. This tends torotate the key 42 as indicated by the arrow r about the pivot point 43in the recess 41. This causes the key 42 to wedge the blade since thedistance from lthe pivot point 43 to the opposite side of the groovedecreases from the point 44 upwardly. Centrifugal force therefore actsto Wedge the key and the blade into the groove 40. The greater thecentrifugal force, the greater is the Wedging action. Preferably thematerial from which the key 42 is made isof softer metal than the bladeitself in order to prevent the key from scoring or otherwise injuringthe blade. It is also preferable to somewhat round the edge of thegroove 40 at 45 adjacent the main portion' of the blade which is understress due to centrifugal force to allow the blade tov freely assume itsnatural contour given to it by centrifugal force ends.

due to rotation.

Fig. 7 shows another` mode of securing the blade In this form, the endsof the blades are enlarged-at 90 and the grooves 40a are spread inwardlyof the groove ridges 91'. The upset orenlarged ends 90 are wider thanthe groove entrance spaces 92 so that the wide ends 90 contact theretaining rings 27 under the facing ledges forming the narrow spaces 92.The enlarged ends 90 of the blades may be introduced into the grooves40a lengthwise of the grooves or in. any other suitable way, and whenoriginally made, the parts `are preferably such that there is only linecontact at 94. When centrifugal force comes into play, the material ofthe blades or the retaining members or both will yield at tlie lines ofcontact 94 and deformation will take place resulting in surface contact.This deformation continues until the contact surfaces have becomeenlarged to such an extent that they are able to sustain the tension inthe blades. In this deformation, the contacting materialis, of course,stretched beyond the yield point. By this means the contact can adjustitself to best suit the structure and the material will give so thatthere is an advantageous distribution of force transmission.

' The blade 34h shown in rig. 7 is thick at the point of attachment andtapers to a minimum thicknessat the most radially outward point. Thisgives a minimum amount of material for the blade since the stress can,in such case, be uniformly distributed. The sheet metal can be rolledto` give this variation of thickness. .An equivalent effect to thetapering may be obtained by the converging blades as shown in Fig. 'la'.It will be understood that both the thickness and the width. may bevaried. It will also be understood that any of various fastening meansmay be used with vany of various kinds of bladng.

It is even conceivable that the blades may be of such soft material asto be entirely limp when lthe turbine is not operating. Blades of thisnature might, for example, be made of fabric `or leather or othermaterial depending upon the kind of expansible fluid, the size of theturbine,

the speed, etc. For steam turbines of any appreciable size, however. llprefer` to use `blades made of stainless steel or other hard materialwhich will not be cut, rusted or otherwise affected by the fluid. Theless the specific weight of the blade material, the less is the stresson the retaining members. A very light material which might weightapproaching permitting the most favorable relation between peripheralvelocity of blade rings and the velocity of steam flowing between theblades. The velocity of the steam between the blades need therefore beonly slightly in excess of the peripheral speed of one rotor relative tothe next rotor.

The shape acquired by a blade, embodying the present invention, when itis rotating, is determined, at any point along the length of the blade,

by the centrifugal force and the distribution of Weight longitudinallyof the blade. The centrifugal force is so great that there issubstantially no deviation of blade form from the natural centrifugalcatenary curve due to steam pressure. Furthermore, blades constructed inaccordance with the invention are less liable to excessive vibrationsthan radial blades supported at one end,

and the retaining members are correspondingly relieved of the adverseinuence of blade vibrations, a factor which is of great importance inturbines of large capacity. The width and edges can be so selected as togive the desired blade angles..

As an analogy, it may be said that the presentinvention applies theprinciple of suspension bridge suspension to turbine constructionwhereby the blades span over lconsiderably longer distances betweencarrying rings than has hitherto been possible. It is well recognized inthe design of suspension bridges that it is of utmost importance thatthe suspended cables be of light and strong material to allow forsuspension over long distances and that the end supports for thesuspended cables and the whole structure increase rapidly in weight andspace if heavier cables are used. Consequently'the blades. according tothis invention should be made of as small cross-sectional area aspossible.

The embodiment shown in Fig. 8 does not diner from the previouslydescribed embodiments so far as concerns the last stage. vln this case,

however, only the last stage 'includes flexible blades. This turbine hasan annulus of stationary guides 48 carried by a stationary web 47 aheadof the rotatable curved blades 34.

Fig. 9 and related figures show the invention applied to a turbinehaving initial axial flow stages and terminal radial ow stages. Theturbine rotor 54 is mounted in bearings 50 and 5l. A stationary casing53 surrounds the rotor 54. The usual packing 55 is provided where therotor passes through the casing. The rotor 54 carries rows of radiallyprojecting blades 56 of known form between which are rows of stationaryguides 57 xed in and projecting inwardly from the casing 53. Steam isadmitted at 58 and passes between the blades an guides causing rotationof the rotor. The :dow of steam past the blades 56 and guides 57 is in agenerally axial direction and in well known axial flow manner. The

blades 56 and'guides 57 `may be termed an axial I may be set intoseparate blade wheels and guide 15@ 3. In a turbine, axially spacedrotatable bladeretaining members, a blade composed of a relatively thinflexible 'strip' of steel having its ends secured to said members andadapted to modify its form under the influence of centrifugal force, andmeans providing a radial flow of4 fluid to said blade.

4. In a turbine, axially spaced rotatable blade retaining members, astructurally flexible `blade which is designed to be flexed by acentrifugal force and which is secured to said members, all

surface lines on said blade extending between said retaining membersbeing curved, and means providing a radial flow of fluid to said blade.

5. In a turbine, axially spaced rotatable blade retaining members, astructurally flexible blade which isA designed to be flexed bycentrifugal force and which is secured to said members, all surfacelines on said blade in radial planes being substantially straight, andmeans providing a radial flow of fluid to said blade.

6. In a turbine, axially spaced rotatable blade retaining members, ablade which is designed to be flexed by centrifugal force and which issecured to said members, all surface lines on said blade extendingbetween said retaining means being curvedy and all surface lines inradial planes being substantially straight, and means providing a radialflow of fluid to said blade.

7. In a turbine, axially spaced blade retaining members, a bladeconsisting of a flexible strip of material secured at its ends to saidmembers, said strip between' said ends being longer than the axialdistance between the retaining members and assuming its operating shapedue to centrifugal force, and means providing a radial flow of fluid tosaid blade.

8. In a turbine, axially spaced blade retaining members, a bladeconsisting of a flexible strip of material secured to said members andshaped by centrifugal force, said strip having inlet and outlet edgesboth longer than the axial vdistance between the retaining members, theinlet edge being shorter than the outlet edge, and means providing aradial flow of fluid to said blade.

9. In a turbine, axially disposed blade retaining members, a flexiblestrip-like blade attached at its ends to said retaining members andflexing to act as a. rigid blade in operation due to centrifugal force,and means'V providing a radial flow of fluid to said blade.

10. In a turbine, axially disposed blade retaining members, a flexiblestrip-like blade attached at its ends to said retaining members curvedand flexed to the form of a centrifugal catenary on.A

rotation, and means providing a radial flow of uidv to said blade. ,A

11. A turbine comprising a pair of rotatable members having groovestherein, a longitudinally curved blade comprising a flexible striphaving its ends in the grooves of said members, and flexed bycentrifugal force, means to retain said blade ends in said grooves, andmeans providing Va radial flow of fluid to said blade.

12. A turbine comprising axially spaced rotatable members having groovestherein, a longitudinally curved blade comprising a flexible striphaving its ends in the grooves vof said members flexed by centrifugalforce, means for wedging said blade ends in said grooves under theinfluence of centrifugal force, and means providing a radial flow offluid to said blade.

13. A turbine' comprising a rotatable member 'having grooves therein, ablade of flexible striplike material having each end bent out of theplane of said strip and disposed in said grooves, and means within eachbend of the blade for retaining the blade in the groove.

14. A turbine comprising a rotatable member having grooves therein, ablade of flexible striplike material having each end bent -out oftheplane of said strip and disposed in said grooves,

and a key in each bend for wedgingthe blade in the groove, saidy keycausing an increased wedging action on increase of centrifugal force.

15; A turbine comprisingl a rotor, axially-disposed retaining ringscarriedvby said rotor, each ring having a series of transverse groovestherein oblique to both its periphery and its `axis of rotation and thegrooves in one ring being of op. posite angular relationship to thegrooves of the other ring, and structurably exible blades having one endfastened in a groove of one ring and the other end fastened in a grooveof theother ring, and means providing a radial flow of fluid to saidblades.

16. A turbine comprising a rotor, axially disposed retaining ringscarried by said rotor, each ring having a series of transverse groovestherein oblique to both its periphery and its axis of rotation and thegrooves in one ring being 'of `opposite angular relationship to thegrooves ofthe other ring, structurablyv flexible, longitudinally curvedblades adapted to change their form under the influence of centrifugalforce spanning the rings and having their ends fastened in said'grooves, and means providing a radial flow of fluid to said blades. 17.A turbine comprising a rotor, axially disposed retaining rings carriedby said rotor, each ring having a series of transverse groovestherein'obliqueto both its periphery and its axis of rotation and thegrooves in one ring being of opposite angular relationship to thegrooves of the other ring, longitudinally curved blades com- 115 prisingrelatively thin flexible strips of sheet steel spanning the rings andhaving their ends fastened in said grooves, and means providing a radialflow of uid to said blades.

18. A turbine comprising a rotor, axially dis- 120 posed retaining ringscarried by said rotor, said rings having grooves therein oblique to bothits periphery and its axis of rotation and the grooves in one ring beingof opposite angular relationship to the grooves of the other ring,longitudinally 128 curved blades comprising relatively thin flexiblestrips spanning said rings, retaining `means for wedging the ends .ofthe blades in the grooves under the influence of centrifugal force, andmeans providing a radial flow of fluid to said blades. 130

19. In a turbine, axially spaced rotatable blade retaining members, staymembers connecting said members for maintaining said retaining members afixed distance apart, structurally ilexible blades comprising flexiblestrips of greater 18| length than said fixed distance attached at oneend to one of said retaining members and at the other end to another ofAsaid retaining members,

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retaining members, stay members connecting said members for maintainingsaid retaining members a fixed distance apart, structurably flexibleblades comprising flexible strips of' greater length than said fixeddistance connected to and spanning said retaining members and obtainingtheir operating shape due to centrifugal force, and means providing 'aradial now of fluid to said v blades.

22. In a turbine, axially spaced rotatable blade retaining members, staymembers connecting said members for maintaining said retaining members afixed distance apart, structurably.

flexible blades of sheet steel of greater length than said fixeddistance connected to and spanning said retaining members and obtainingtheir operating shape due to centrifugal force, the ends of the bladesbeing connected to the retaining members obliquely to the axis ofrotation and at opposite angularity with respect to the axis ofrotation, and means providing a radial flow of uid to said blades.

23. In a turbine, axially spaced rotatable blade retaining members,-stay members connecting said members for maintaining said retainingmembers a xed distance apart, structurally flexible blades comprisingflexible strips of sheet steel of greater length than said fixeddistance spanning said retaining members and obtaining their operativeshape by centrifugal force, grooves of opposite Obliquity in saidretaining members for receiving the ends of the blades, and retainingkeys for Wedging the ends of the blades in said grooves.

24. A turbine blade comprising a flexible strip of metal, said bladebeing structurally flexible to respond to and assume its operative shapedue to i centrifugal force, and means providing a radial flow of fluidto said blade.

plurality of axial flow blades and guides secured to said rotor and saidcasing respectively, a plurality of axially spaced rings connected tosaid rotor, and a plurality of longitudinally curved radial now bladesconnected to said rings and constituting low pressure stages of saidturbine.

28. A turbine comprising a rotor, a casing, a plurality of axial flowblades and guides secured to said rotor and said casing respectively, aplurality of axially spaced rings vconnected to said rotor, and aplurality of structurally flexible and longitudinally curved radial flowblades secured to and spanning said rings at the low pressure end of theturbine. y

29..A turbine comprising a rotor, a casing, a plurality of axial owblades and guides secured to said rotor and said casing respectively, aplurality of. axially spaced rings connected to said rotor, and aplurality of radial flow blades of longitudinally curved and flexiblestrips secured mentioned rotor, each of said radial flow rotorsplurality of axial flow blades and guides secured to said rotor and saidcasing respectively, and a plurality of radial now rotors secured tothefirstmentioned rotor, each of said radial flow rotors comprising axiallyspaced rings, stays -between said rings and curved blades of sheet steelconnected to said rings.

33. A turbine comprising-a rotor, a casing, a plurality of axial flowblades and guides secured to said rotor and said casing respectively,and a plurality of radial flow rotors secured to the firstmentionedrotor, each of said radial flow rotors comprising axially spaced rings,stays between said rings, curved blades connected to said 'ringsand/axially extending guides between said radial flow rotors secured tosaid casing.

34. A turbine comprising a rotor, a casing, a plurality of axial nowblades and guides secured to said rotor and said casing respectively,and a plurality of radial flow rotors secured to the firstmentionedrotor, each of said radial flow rotors Acomprising axially spaced rings,stays between said rings, curved flexible blades connected to said ringsand axially extending guides between said radial flow rotors secured tosaid casing.

35. In a turbine, in combination with means providing a radial flow offluid, a rotatable blade retaining member and a blade adapted to beflexed by centrifugal force loosely secured at each end in saidretaining member.

36. In a turbine, in combination with means providing a radial flow offluid, axiallyspaced rotatable blade retaining members and a bladeconsisting of a exible strip of metal loosely secured at its oppositeends to said members.

37. In a turbine, axially spaced rotatable blade retaining membershaving transverse grooves therein with narrow entrance spaces, andflexible strip-like blades having enlarged heads at their opposite ends,said blades adapted to be flexed by centrifugal force and having saidheads 1ocated in said grooves `and contacting the sides of the grooveson surfaces determined ,by deformation of material due tocentrifugal-force.

38. A turbine blade comprising a fiemfble arcuate strip of materialflexed to an arcuate form and readily deformable under the action ofcentrifugal force, in combination with means providing a radial low ofuid to said blade.

39. A turbine comprising a rotor, a casing, a plurality of axial flowblades and guides secured to said rotor vand said casing respectively, aplurality of radial flow rotors secured to the rst mentioned rotor, eachof said radial flow rotors comprising axially spaced rings, staysbetween said rings. and curved flexible blades connected to said rings.

40. in a turbine, axially-spaced rotatable blade retaining members, aflexible blade designed to be flexed by centrifugal action and securedto said members, and means providing a radial ow of fluidy to saidblades.

41. In a turbine, axially disposed blade retaining members, and aplurality of flexible striplike blades attached at their ends to saidretaining members, said blades overlapping for a portion of their lengthadjacent their ends.

42. In a turbine, axially disposed blade retaining members, and aplurality of flexible striplikeblades attached at their ends to saidretaining members, each blade overlying an adjacent blade for only thatportion of its length which is near a retaining member.

43. In a turbine, axially disposed blade retaining members, and aplurality of flexible striplike blades attached at their ends to saidretaining members, said blades being of increasing width near saidretaining members whereby said blades overlap at that portion of theirlength which is adjacent their attachments to said members.

44. In a turbine, axially disposed blade retaining members provided withtransverse grooves having narrow openings and a flexible strip-likebladesecured at'its ends in said grooves, saidA blade" having enlargedends adapted to make a line contact with each opposite wall of a groovewhen installed and to make a surface contact with each opposite wall ofa groove under the action of centrifugal force.

45. In a turbine, axially disposed blade retaining members provided withtransverse grooves having narrow openings and a flexible strip-likeblade secured at its endsy in said grooves, the contacting surfaces ofsaid blade ends andl grooves being so shaped as to initially form linecontacts and to deform into surface contacts under the action of thecentrifugal forces acting on said blades.

46. In a turbine, axially disposed blade retaining members provided withtransverse? grooves having narrow openings and a flexible strip-likeblade secured at its ends in said grooves, the contacting surfaces ofeach blade andthe Wall of its groove including at least one curvedsurface which makes aline contact with its opposed surface when theblade is installed but which in.-

creases its area of contact under the action'of

